Tunnel waterproofing method

ABSTRACT

A tunnel waterproofing method comprises spraying a primary coating of concrete onto the excavation surface of a tunnel, installing thereon a waterproofing sheet having an adhesive layer operative to bond with concrete, and spraying a secondary coating of concrete against the adhesive side of the waterproofing sheet. Preferably, a buffer water conducting sheet is established between the primary concrete coating sprayed onto the excavation surface and the waterproofing sheet.

DETAILED DESCRIPTION OF THE INVENTION

1. Technological Field of the Invention

This invention relates to a waterproofing method for tunnels.

In this invention, paste, mortar and concrete are used as general termsto refer to cement concrete.

2. Prior Art

The principal tunnel construction method in Japan at present is the NATMmethod. The NATM construction method is a method in which primarycoating is performed by means of spray mortar or spray concreteimmediately after excavation of the tunnel to prevent falling of rockand water leakage in the excavation region, after which a secondarycoating concrete is applied to stabilize the tunnel by maintainingtunnel strength. At this time, a waterproofing sheet is installed forthe purpose of waterproofing and insulation between the primary coatingconcrete and the secondary coating concrete so that leakage of waterinto the tunnel can be prevented and so that cracks due to binding ofthe secondary coating concrete to earth mounds or movement of earthmounds can be prevented. Most recently, tunnel excavation has beenperformed by tunnel boring machines (TBM construction method) andwaterproofing sheets are installed for the same objectives.

Further, because the width of the sheet is narrow, being 1 to 2 m, thereare the problems that it takes great effort and trouble and it isuneconomical when the ends of the waterproofing sheets are overlaid oneach other and joined by welding.

There is the further problem that water infiltrates between thewaterproofing sheets and the secondary coating concrete due to damage ofthe waterproofing sheet functionally by poorly welded components and byirregularities in the excavation surface so that waterproofing capacityis not obtained.

[Problems the Invention is Intended to Solve]

When the thickness of the waterproofing sheets is increased in order toprevent damage to the waterproofing sheets, there are the problems thatwelding of the ends of the waterproofing sheets becomes difficult andthat the mass of the waterproofing sheets is increased, with the resultthat actual execution characteristics become even poorer.

The inventors conducted various studies of the aforementioned problems.As a result, they perfected this invention by discovering a tunnelwaterproofing construction method whereby a waterproofing sheet that isadhesive to the secondary coating cement concrete is installed on theprimary spray cement concrete surface before installing the secondarycoating cement concrete, and, in which, by making it into a singleentity with the secondary coating cement concrete, infiltration of waterbetween the waterproofing sheet and the secondary coating concretebecause of poor weld sites and damage of the ends of the waterproofingsheets is prevented, leakage of water is prevented even when cracks aregenerated in the secondary coating cement concrete and waterproofingcapacity can be greatly increased.

[Means for Solving the Problems]

Specifically, this invention is a tunnel waterproofing methodcharacterized in that a primary spray cement concrete is sprayed on theexcavation surface of the tunnel, after which a secondary coating cementconcrete and a waterproofing sheet having adhesiveness are installed onsaid primary spray cement concrete surface such that the secondarycoating cement concrete is established on said waterproofing sheetsurface, [or] a tunnel waterproofing method characterized in that aprimary spray cement concrete is sprayed on the excavation surface ofthe tunnel, after which a buffer-water conducting layer is establishedin said primary spray cement concrete surface, a secondary coatingcement concrete and a waterproofing sheet having adhesiveness areinstalled on said secondary coating cement concrete such that thesecondary coating cement concrete is established on said waterproofingsheet surface; and a tunnel waterproofing method further characterizedin that the waterproofing sheet is a multilayer waterproofing sheet thathas a layer that has adhesiveness with the installed secondary coatingcement concrete.

[Mode of Execution of the Invention]

We shall now describe this invention in detail.

This invention is a construction method in which the waterproofing sheetand the tunnel are made into a single entity by spraying, preferably, afast-drying cement concrete onto the excavated tunnel surface, afterwhich a waterproofing sheet that is adhesive with the secondary coatingcement concrete is installed. This waterproofing sheet allows forfollow-up of cracking of cement concrete due to drying and contractionof the secondary coating cement concrete and of earth mounds aftercompletion. By making the cement concrete and the waterproofing sheetinto a single entity, contact with water occurs only in sites that aredamaged even if damage to the waterproofing sheets occurs. For thisreason, leakage of water does not occur as long as cracks do not developin the secondary coating concrete in the region of the sheet damage.Therefore, water leakage is greatly decreased and excellentwaterproofing capacity is obtained. Further, water leakage does notoccur as with conventional waterproofing sheets as a result of waterinfiltrating between the waterproofing sheet and the secondary coatingcement concrete, of impairment of the waterproofing capacity of thetunnel as a whole, and of cracks in the secondary coating cementconcrete. Moreover, because a waterproofing sheet that is made into asingle entity with the secondary coating cement concrete prevents waterleakage with good follow-up capacity and without damage occurring evenwhen cracks are generated in the tunnel itself, waterproofing capacityis increased to a great extent by comparison to conventionalwaterproofing construction methods.

Examples of waterproofing sheets that are adhesive with secondarycoating cement concrete include uncrosslinked rubber sheets such asisoprene rubber and natural rubber.

The waterproofing sheet that is adhesive with the secondary coatingcement concrete may also contain antioxidants, ultraviolet radiationabsorbents and tackiness-decreasing agents.

In this invention, it is desirable to laminate the layer havingadhesiveness with the secondary cement concrete with a polymeric sheetfrom the standpoint of increasing the insulation effect with thesecondary coating cement concrete if it has been bound with the earthmound. When a layer that is adhesive with the secondary coating cementconcrete and a multilayer waterproofing sheet that is laminated with apolymeric sheet are used, they are installed so that the primary spraycement concrete surface side and the polymeric sheet are in contact andthe secondary coating cement concrete is installed on the waterproofingsheet surface side that is adhesive with the secondary coating cementconcrete.

Examples of the material of the polymeric sheet can include high-densitypolyethylene, low-density polyethylene, copolymers of ethylene vinylacetate (EVA) and polypropylene. Of these, high-density polypropylene ispreferable from the standpoint of insulation effect, strength, crackfollow-up capacity and price.

In this invention, a buffer-water conducting layer may be establishedbefore installing the waterproofing sheet that is adhesive with thesecondary coating cement concrete for the purpose of increasing theinsulation effect, decreasing water pressure in sites in which there isa great deal of groundwater and increasing the waterproofing effect.Examples of buffer-waterproofing layers can include layers that areformed by spraying a fibrous substance such as pulp nonwoven fabrics offibers such as polyester fibers and polypropylene and plates orirregular shapes.

The waterproofing construction method can be used in the bedding portionof the tunnel and displays great effectiveness in preventing waterleakage from the bedding component.

There are no particular limitations on the method of affixing thewaterproofing sheet, nonwoven fabric and plates of irregular shape tothe primary spray cement concrete surface and adhesive agents and rivetsmay be used.

After the waterproofing sheet that is adhesive to the secondary coatingcement concrete has been installed in this way, the secondary coatingcement concrete is applied and construction is completed.

EXAMPLES

We shall now describe this invention in detail on the basis of examples.

Example 1

A U-shaped simulation tunnel having openings of 4 m, a height of 3.5 mand a length of 3 m was made. Irregularities of the tunnel earth moundsurface were presumed in the simulation tunnel and fifteen concreteblocks of 15 cm in width, 20 cm in height and 20 cm in length wereinstalled at suitable intervals to form an irregular surface.

Fast-drying mortar was used as the primary spray mortar and was sprayedso that the fast-drying mortar was 10 cm in thickness.

After spraying, a multilayer waterproofing sheet having adhesiveness tothe secondary coating concrete (brand name, “Preprufe 300,” manufacturedby the Grace Construction Products Company of the United States; atwo-layer sheet comprised of two layers, a layer having adhesiveness toconcrete and a polyethylene layer; 2.7 mm in thickness) was affixed byriveting to the primary spray mortar surface. Following that, thesecondary coating concrete was applied to a thickness of 30 cm. Tosimulate damage to the multilayer waterproofing sheet, cuts were made ina part of it.

Twenty-eight days after the secondary coating concrete was established,a test sample was cut out by boring and adhesiveness with the concretewas checked. The secondary coating concrete and the waterproofing sheetwere in good contact and were a single entity. The peeling strength ofthe secondary coating concrete and the waterproofing sheet was greaterthan 0.9 N/mm.

A single entity with the secondary coating concrete was also wellmaintained in the region of the cut, with the cut in the concrete beingin a linear pattern of less than 2 mm. A static water pressure of 60 mwas applied in the gap between the primary spray concrete and themultilayer waterproofing sheet. However, water did not enter into thegap between the multilayer waterproofing sheet and the secondary coatingconcrete, with good waterproofing capacity being shown.

Because the multilayer waterproofing sheet that was used hadadhesiveness, the multilayer waterproofing sheets could be adhered toeach other satisfactorily simply by superimposing the ends of themultilayer waterproofing sheets on each other. For this reason,execution capacity was extremely good and an excellent value of 1.7 N/mmwas obtained for adhesive strength of the superimposed parts.

To simulate cracks in the tunnel, stress was applied to the secondarycoating concrete and cracks were made. No abnormalities were seen in themultilayer waterproofing sheet.

The test methods for the various physical properties were as follows.

Adhesive strength with the concrete: In accordance with ASTM D 903 (90degree peeling strength). Adhesive strength of superimposed portions: Inaccordance with ASTM D 1876 (Determinations in the case in whichmultilayer waterproofing sheets are superimposed).

Example 2

The same procedure was carried out as in Example 1 except that themultilayer waterproofing sheet having adhesiveness with the secondarycoating concrete that was used was a product of the brand name“Santacket* Sheet” (isoprene rubber waterproofing sheet, a nonwovenfabric lined product, manufactured by Hayakawa Rubber).

*Phonetic spelling—Trans. note.

Twenty-eight days after the secondary coating concrete was established,a test sample was cut out by boring and adhesiveness with the concretewas checked. The secondary coating concrete and the waterproofing sheetwere in good contact and were a single entity.

However, it was more difficult to join the ends of the multilayerwaterproofing sheets than in Example 1 and workability was also somewhatdifficult.

Comparative Example 1

The same procedure was carried out as in Example 1 except that awaterproofing sheet made of EVA (which did not have adhesiveness withthe secondary coating concrete) was used instead of a multilayerwaterproofing sheet having adhesiveness with the secondary coatingconcrete.

When pressure corresponding to 30 m of static water pressure was appliedbetween the primary spray mortar and waterproofing sheet, it was foundfrom the cracks in which damage was presumed that a large quantity ofwater entered into the gap between the waterproofing sheet and thesecondary coating concrete and that properties of a waterproofing sheetwere not obtained.

[Effect of the Invention]

By making the secondary coating cement concrete and the waterproofingsheets into a single entity using the waterproofing sheets of thisinvention having adhesiveness with the secondary coating cementconcrete, water does not infiltrate between the gap between thewaterproofing sheets and the secondary coating concrete and excellentwaterproofing capacity can be assured even if a part of thewaterproofing sheets is damaged.

Further, the crack follow-up of the waterproofing sheets of thisinvention is good, the waterproofing sheets are not damaged andexcellent waterproofing capacity can be assured even if cracks developin the secondary coating cement concrete. Even if by any chance thecrack width is large and damage of the waterproofing sheet occurs,because the other portions of the waterproofing sheet are a singleentity with the secondary coating cement, water does not infiltrate intothe gap between the waterproofing sheets and the secondary coatingconcrete; therefore, the industrial benefits are extremely great.

What is claimed is:
 1. A tunnel waterproofing method comprising:spraying a primary layer of cement concrete on the excavation surface ofthe tunnel, establishing on the primary cement concrete layer abuffer-water conducting layer by affixing a nonwoven fabric, a fibrousmaterial, or plates of irregular shapes, establishing on saidbuffer-water conducting layer a waterproofing membrane having a plasticor rubber sheet and an adhesive layer operative to adhere with asecondary coating concrete applied on said waterproofing membrane, andspraying onto said waterproofing membrane a secondary coating of cementconcrete, thereby achieving waterproofing of the tunnel.
 2. The tunnelwaterproofing method as described in claim 1, wherein said waterproofingmembrane has a polymeric sheet comprising high-density polyethylene, lowdensity polyethylene, copolymers of ethylene vinyl acetate,polypropylene, or mixture thereof.
 3. The tunnel waterproofing method ofclaim 2 wherein said polymeric sheet is polyethylene.
 4. The tunnelwaterproofing method of claim 1 wherein said sheet comprises anuncrosslinked rubber.
 5. The tunnel waterproofing method of claim 4wherein said uncrosslinked rubber comprises isoprene rubber, naturalrubber, or mixture thereof.
 6. The tunnel waterproofing method of claim1 wherein said waterproofing membrane is formed by superimposing ends ofadjacent waterproofing sheets on each other.
 7. The tunnel waterproofingmethod of claim 1 wherein said establishing of a buffer water conductinglayer comprises spraying a fibrous substance.
 8. The tunnelwaterproofing method of claim 1 wherein said establishing of a bufferwater conducting layer comprises spraying fibers comprising polyester,polypropylene, or mixture thereof.
 9. The tunnel waterproofing method ofclaim 1 wherein said establishing of a buffer-water conducting layercomprises affixing plates of irregular shapes.
 10. The tunnelwaterproofing method of claim 1 wherein said establishing of abuffer-water conducting layer comprises affixing a nonwoven fabric usingan adhesive or rivets.
 11. The tunnel waterproofing method of claim 1wherein said tunnel is a U-shaped tunnel.